import java.util.ArrayList;

public class Test {
    public static void main(String[] args) {

        //pen是pencil的父类
        Pen pen = new Pen();
        Pencil pencil = new Pencil();

        //pencils 和 pens  有父子的这种继承关系嘛？
        ArrayList<Pencil> pencils = new ArrayList<>();
        ArrayList<Pen> pens = new ArrayList<>();


    }
}

class Pen{}

class Pencil extends Pen{}
